Use of spongosine for the treatment of pain

ABSTRACT

Use of spongosine (2-methoxyadenosine) as an analgesic, in particular for the treatment of hyperalgesia, is described.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. application Ser. No.10/537,564, filed Aug. 28, 2006, which claims priority to internationalapplication number PCT/GB2003/005379, filed Dec. 9, 2003, which claimsthe benefit of priority of British application number 0228723.3, filedDec. 9, 2002. The disclosures of the prior applications are consideredpart of (and are incorporated by reference in) the disclosure of thisapplication.

This invention relates to an analgesic and to methods of preventing,treating, or ameliorating pain using the analgesic.

Pain has two components, each involving activation of sensory neurons.The first component is the early or immediate phase when a sensoryneuron is stimulated, for instance as the result of heat or pressure onthe skin. The second component is the consequence of an increasedsensitivity of the sensory mechanisms innervating tissue which has beenpreviously damaged. This second component is referred to ashyperlagesia, and is involved in all forms of chronic pain arising fromtissue damage, but not in the early or immediate phase of painperception.

Thus, hyperalgesia is a condition of heightened pain perception causedby tissue damage. This condition is a natural response of the nervoussystem apparently designed to encourage protection of the damaged tissueby an injured individual, to give time for tissue repair to occur. Thereare two known underlying causes of this condition, an increase insensory neuron activity, and a change in neuronal processing ofnociceptive information which occurs in the spinal cord. Hyperalgesiacan be debilitating in conditions of chronic inflammation (e.g.rheumatoid arthritis), and when sensory nerve damage has occurred (i.e.neuropathic pain).

Two major classes of analgesics are known: (i) non steroidalanti-inflammatory drugs (NSAIDs) and the related COX-2 inhibitors; and(ii) opiates based on morphine. Analgesics of both classes are effectivein controlling normal immediate, or nociceptive pain. However, they areless effective against some types of hyperalgesic pain, such asneuropathic pain. Many medical practitioners are reluctant to prescribeopiates at the high doses required to affect neuropathic pain because ofthe side effects caused by administration of these compounds, and thepossibility that patients may become addicted to them. NSAIDs are muchless potent than opiates, so even higher doses of these compounds arerequired. However, this is undesirable because these compounds causeirritation of the gastro-intestinal tract.

Adenosine A1 receptor agonists are known to act as powerful analgesics(Sawynok, Eur J. Pharmacol. (1998) 347, 1-11), and adenosine A2Areceptor agonists are known to act as anti-inflammatory agents. However,development of adenosine-based therapies has generally been precludedbecause they have unacceptable side effects. Selective A1 receptoragonists cause bradycardia, and A2A receptor agonists cause widespreadvasodilation with consequent hypotension and tachycardia.

There is, therefore, a need to provide analgesics which are sufficientlypotent to control pain perception in neuropathic, inflammatory, andother hyperalgesic syndromes, and which do not have serious side effectsor cause patients to become addicted to them.

Spongosine is a compound that was first isolated from the tropicalmarine sponge, Cryptotethia crypta in 1945 (Bergmann and Feeney, J. Org.Chem. (1951) 16, 981, Ibid (1956) 21, 226). Spongosine was the firstmethoxypurine found in nature, and is also known as 2-methoxyadenosine,or 9H-purin-6-amine, 9-α-D-arabinofuranosyl-2-methoxy.

The first biological activities of spongosine were described by Bartlettet al. (J. Med. Chem. (1981) 24, 947-954) who showed that this compoundhas muscle relaxant, hypothermic, hypotensive, and anti-inflammatoryactivity in rats (anti-inflammatory activity was assessed by inhibitionof carrageenan-induced oedema in a rat paw).

The affinity of spongosine for the rat adenosine A1 and A2A receptorshas been determined. The Kd values obtained were 340 nM for the A1receptor and 1.4 μM for the A2A receptor (Daly et al., Pharmacol. (1993)46, 91-100). In the guinea pig, the efficacy of spongosine was tested inthe isolated heart preparation and the EC50 values obtained were 10 μMand 0.7 μM for the adenosine A1 and A2A receptors, respectively (Ueedaet al J Med Chem (1991) 34, 1334-1339). In the early 1990s the otheradenosine receptors (the A2B and A3 receptors) were cloned, but theactivity of spongosine at these receptors was never investigated. Thelow potency and poor receptor selectivity of this compound led to itbeing largely ignored as more and more potent and receptor selectivenovel compounds were synthesised.

It has surprisingly been found that spongosine when administered tomammals gives significant pain relief in conditions of increased painsensitivity (such as neuropathic and inflammatory hyperalgesia), withoutcausing the significant side effects expected from use of purinereceptor agonists.

According to the invention there is provided use of spongosine in themanufacture of a medicament for the prevention, treatment, oramelioration of pain.

The term “spongosine” is used herein to include spongosine free base, ora pharmaceutically acceptable salt of spongosine.

Use of spongosine according to the invention is particularly concernedwith the prevention, treatment, or amelioration of pain other than theearly or innnediate phase of pain as described above, and is especiallyconcerned with the prevention, treatment, or amelioration ofhyperalgesia.

There is also provided according to the invention a method ofpreventing, treating, or ameliorating pain (in particular hyperalgesia)which comprises administering spongosine to a subject in need of suchprevention, treatment, or amelioration.

Spongosine has surprisingly been found to be effective in inhibitingpain perception in mammals suffering from neuropathic and inflammatorypain even when administered at doses expected to give concentrationswell below those known to activate adenosine receptors. Thus, spongosinecan treat neuropathic and inflammatory pain without causing thesignificant side effects associated with administration of otheradenosine receptor agonists.

No analgesic effect on normal physiological nociception was observedafter administration of spongosine.

Because hyperalgesia is a consequence of tissue damage, either directlyto a sensory nerve, or to tissue innervated by a sensory nerve, thereare many diseases or conditions in which pain perception includes acomponent of hyperalgesia.

Spongosine can be used as an anti-hyperalgesic for the prevention,treatment, or amelioration of hyperalgesia caused as a result ofneuropathy, including bowel pain, back pain, cancer pain, my pain,phantom limb pain, post-operative pain, diabetic neuropathy,polyneuropathy, post-herpes neuralgia, and trigeminal neuralgia.

Other diseases or conditions involving damage to sensory nerves whichcontain a component of neuropathic pain include, pancreatic pain,pelvic/perineal pain, lower back pain, chest pain, cardiac pain, pelvicpain/PID, joint pain (for example, associated with tendonitis, bursitis,acute arthritis), neck pain, obstetric pain (labour orCaesarean-Section), chronic neuropathic pain, failed back surgery pain,post physical trauma pain (including pain caused by a gunshot wound, aroad traffic accident, or a burn), scar tissue pain, acute herpes Zosterpain, acute pancreatitis breakthrough pain (cancer), or for theprevention, treatment, or amelioration of neuropathic or other paincaused by, or associated with, fibromyalgia, myofascial pain syndrome,osteoarthritis, rheumatoid arthritis, sciatica or lumbar radiculopathy,spinal stenosis, temporomandibular joint disorder, renal colic,dysmenorrhoea/endometriosis.

Spongosine can be used as an anti-hyperalgesic for the prevention,treatment, or amelioration of hyperalgesia caused as a result ofinflammatory disease, including bowel pain, back pain, cancer pain,fibromyalgia, post-operative pain, osteoarthritis, and rheumatoidarthritis.

Other diseases or conditions in which hyperalgesia plays a prominentrole in pain perception because they are associated with chronicinflammation include other arthritic conditions such as rheumatoidspondylitis, gouty arthritis, or asthma, chronic obstructive pulmonarydisease, fibrosis, multiple sclerosis, sepsis, septic shock, endotoxicshock, gram negative shock, toxic shock, hemorrhagic shock, adultrespiratory distress syndrome, cerebral malaria, organ transplantrejection, pain secondary to cancer, my, chronic pulmonary inflammatorydisease, silicosis, Ulmonary sarcosis, bone resorption diseases,reperfusion injury, graft v. host rejection, multiple sclerosis,myasthenia gravis, allograft rejections, fever and myalgia due toinfection, AIDS related complex (ARC), keloid formation, scar tissueformation, Crohn's disease, ulcerative colitis and pyresis, :irritablebowel syndrome, osteoporosis, cerebral malaria, bacterial meningitis, oradverse effects from amphotericin B treatment, interleukin-2 treatment,OKT3 treatment, or GM-CSF treatment.

The pain associated with many of the above diseases or conditions arerelatively resistant to NSAIDs and opiates.

It will be appreciated that spongosine may be administered together witha pharmaceutically acceptable carrier, excipient, or diluent.

The appropriate dosage of spongosine will vary with the age, sex, andweight of the subject being treated, and the route of administration.

Preferably spongosine is administered at a dose that gives rise toplasma concentrations one fifth to one thousandth, preferably one fifthto one hundredth, of the minimum plasma concentration of spongosine thatgives rise to bradycardia, hypotension or tachycardia side effects inanimals of the same species as the subject to which the dose is to beadministered.

Alternatively, it is preferred that spongosine is administered at a dosethat is one fifth to one fiftieth, preferably one fifth to one tenth, ofthe minimum dose of spongosine that gives rise to bradycardia,hypotension or tachycardia side effects in animals of the same speciesas the subject to which the dose is to be administered.

Preferably spongosine is administered at a dose of less than 6 mg/kg,and preferably at least 0.01 mg/kg, more preferably at least 0.05 mg/kg,most preferably at least 0.1 mg/kg. More preferably spongosine isadministered at a dose of 0.1 to 1 mg/kg, or 0.2 to 1 mg/kg.

Thus, preferred doses for a 70 kg human subject are less than 420 mg,preferably at least 0.7 mg, more preferably at least 3.5 mg, mostpreferably at least 7 mg. More preferably 7 to 70 mg, or 14 to 70 mg.

Spongosine may be administered by any suitable route, preferably orally,parenterally, sublingually, transdennally, intrathecally, ortransmucosally.

Preferably spongosine is administered at a frequency of 2 or 3 times perday.

It has also been found that additive analgesic effects can be obtainedif spongosine is administered with another analgesic agent. Thus,spongosine and the other analgesic agent can be administered to obtain adesired level of analgesic effect, each at a lower dose than would berequired to achieve that level if either agent was administered alone.Because lower doses of each agent can be administered, side effectsassociated with administration of higher doses of the agents arereduced. Alternatively, an increased level of analgesic effect can beobtained by administering spongosine and the other analgesic agent athigher doses.

The preferred dosage of spongosine when administered with anotheranalgesic agent is lower than a preferred dosage specified above foradministration of spongosine alone.

It is believed that an additive analgesic effect is achieved if theother analgesic agent does not act in the same way as spongosine.Suitable other analgesic agents that may be administered with spongosineinclude opioid receptor agonists and partial agonists (such as morphine,diamorphine, fentanyl, buprenorphine, codeine, or derivatives thereof),cyclooxygenase inhibitors (such as aspirin, paracetamol, ibuprofen,diclofenac, or derivatives thereof), sodium or calcium channelmodulators (such as lignocaine, or gabapentin), or Selective SerotoninReuptake Inhibitors (SSRI's) (such as paxil).

Example 4 below shows that “the anti-hyperalgesic properties ofspongosine are unaffected by co-administration of the opioid receptorantagonist naloxone indicating that spongosine does not act via anopioid receptor. Example 5 below demonstrates the additive analgesiceffects of co-administration of spongosine and gabapentin. Gabapentin iseffective against neuropathic pain. It is expected that other analgesicagents that are designed to treat neuropathic pain may have additiveanalgesic effects with spongosine. Such agents include topamax,pregabalin, ziconitide, and cannabinoid derivatives.

Embodiments of the invention are described in the following exampleswith reference to the accompanying drawings in which:

FIG. 1 shows the anti-hyperalgesic actions of spongosine (0.6 mg/kgp.o.) on carrageenan induced hyperalgesia. A: time course (*p<0.05,**p<0.01 versus vehicle (Sidak's), p>0.05 versus BL over 5 hrs forSpongosine and IND (Dunnett's)); B: dose dependency of theanti-hyperalgesic effect;

FIG. 2 shows the anti-hyperalgesic actions of spongosine (0.6 mg/kgp.o.) in the chronic constriction injury model of neuropathic pain(*p<0.05, **p<0.01 vs veh (ANOVA Sidak's);

FIG. 3 shows the effect of spongosine (0.6 mg/kg p.o.) on A: bloodpressure in normal rats; B: heart rate;

FIG. 4 shows the effect of spongosine (0.6 mg/kg p.o.) in the presenceand absence of naloxone in the chronic constriction injury model ofneuropathic pain; and

FIG. 5 shows the additive effect of spongosine and gabapentin in thechronic constriction injury model of neuropathic pain.

EXAMPLES Example 1

FIG. 1: A. Spongosine (0.624 mg/kg p.o.) inhibits carrageenan (CGN)induced thermal hyperalgesia (CITH) with comparable efficacy toindomethacin (3 mg/kg, po). B. Concentration-response relationship forSpongosine at 3 hrs post dosing. Carrageenan (2%, 10 microlitres) wasadministered into the right hind paw. A heat source was placed close tothe treated and untreated hind paws, and the difference in the pawwithdrawal latencies is shown. Spongosine was administered at the sametime as carrageenan.

Example 2

FIG. 2: Spongosine (0.624 mg/kg p.o.) inhibits thermal hyperalgesiacaused by chronic constriction injury of the rat sciatic nerve. Underanaesthesia the sciatic nerve was displayed in the right leg, and fourloose ligatures tied round the nerve bundle. After approximately twoweeks the rats developed thermal hyperalgesia in the operated leg asjudged by the difference in paw withdrawal latencies of the right andleft paws. Administration of spongosine reduced the hyperalgesia asshown by the reduction in the difference between the withdrawallatencies. Spongosine was as, or more, effective than carbamazepine(CBZ, 100 mg/kg s.c.)

Example 3

FIG. 3: Spongosine (0.624 mg/kg p.o.) has no significant effect on bloodpressure or heart rate. An implantable radiotelemetry device was placedin the abdominal cavity of 6 rats per group. The pressure catheter ofthe device was inserted in the abdominal aorta and two electrodestunnelised under the skin in a lead II position (left side of abdominalcavity/right shoulder). Individual rats were placed in their own cage ona radioreceptor (DSI) for data acquisition. A: blood pressure, B; heartrate.

Example 4

FIG. 4: Spongosine (1.2 mg/kg p.o.) inhibits static allodynia caused bychronic constriction injury of the rat sciatic nerve, both in thepresence and absence of naloxone (1 mg/kg s.c.). Under anaesthesia thesciatic nerve was displayed in the right leg, and four loose ligaturestied round the nerve bundle. After approximately two weeks the ratsdeveloped static allodynia in the operated leg as judged by thedifference in paw withdrawal thresholds of the right and left paws.Administration of spongosine reduced the hyperalgesia as shown by theincreased paw withdrawal threshold (PWT) in the presence and absence ofnaloxone. Veh: vehicle.

Example 5

FIG. 5: Spongosine and gabapentin inhibit static allodynia caused bychronic constriction injury of the rat sciatic nerve. Spongosine andgabapentin were administered (p.o.) in different proportions asindicated in the drawing. The total dose administered is shown on thehorizontal axis, and the paw withdrawal threshold (PWT) on the verticalaxis. The predicted anti-hyperalgesic effect (derived from the doseresponse curves obtained with each agent alone) if the effects of thetwo compounds are additive is shown (). The observed effects areindicated by (▪). It is apparent that the observed effects are notsignificantly different from those predicted by additivity.

Spongosine is effective in inhibiting pain perception in mammalssuffering from neuropathic and inflammatory pain even when administeredat doses expected to give concentrations well below those mown toactivate adenosine receptors. At these doses it can be seen that neitherthe heart A1 receptors nor the vascular A2A receptors are sufficientlystimulated to cause a change in the cardiovascular status of theanimals.

Spongosine can therefore be used as an anti-hyperalgesic which can beadministered orally for the treatment of hyperalgesia caused as a resultof neuropathy or inflammatory disease, including bowel pain, back pain,cancer pain, fibromyalgia, my pain, phantom limb pain, osteoarthritis,rheumatoid arthritis, post-herpes neuralgia, trigeminal neuralgia,polyneuropathy, diabetic neuropathy and postoperative pain.

1.-31. (canceled)
 32. A pharmaceutical composition for administration toa human subject, comprising spongosine or a pharmaceutically acceptablesalt thereof and a pharmaceutically acceptable carrier, excipient ordiluent.
 33. A dose of a pharmaceutical composition for administrationto a human subject comprising spongosine or a pharmaceuticallyacceptable salt thereof and a pharmaceutically acceptable carrier,excipient or diluent, wherein the dose comprises an amount of spongosineor a pharmaceutically acceptable salt thereof that gives rise to plasmaconcentrations that are one fifth to one thousandth of the minimumplasma concentration of spongosine that gives rise to bradycardia,hypotension or tachycardia side effects in the subject.
 34. A doseaccording to claim 33 wherein the dose comprises less than 6 mgspongosine or a pharmaceutically acceptable salt thereof per kg of thesubject.
 35. A dose according to claim 33 or 34, wherein the dosecomprises at least 0.01 mg spongosine or a pharmaceutically acceptablesalt thereof per kg of the subject.
 36. A dose of a pharmaceuticalcomposition for administration to a human subject comprising spongosineor a pharmaceutically acceptable salt thereof and a pharmaceuticallyacceptable carrier, excipient or diluent, wherein the dose comprisesless than 420 mg spongosine or a pharmaceutically acceptable saltthereof.
 37. A dose according to claim 36 comprising at least 0.7 mgspongosine or a pharmaceutically acceptable salt thereof.
 38. A doseaccording to claim 36 comprising 70 mg spongosine, or a pharmaceuticallyacceptable salt thereof.
 39. A pharmaceutical composition foradministration to a human subject, comprising spongosine or apharmaceutically acceptable salt thereof, another analgesic agent and apharmaceutically acceptable carrier, excipient or diluent.
 40. Apharmaceutical composition according to claim 39, wherein the otheranalgesic agent does not act at adenosine receptors.
 41. Apharmaceutical composition according to claim 39, wherein the otheranalgesic agent is an opioid receptor agonist or partial agonist, acyclooxygenase inhibitor, a sodium or calcium channel modulator, or aselective serotonin reuptake inhibitor.
 42. A pharmaceutical compositionaccording to claim 41, wherein the other analgesic agent is gabapentin.